An Organic Light Emitting Diode (OLED) typically comprises an anode and a cathode, and a light emitting unit located between the anode and the cathode. According to different numbers of light emitting units, OLEDs may be divided into a one-unit OLED and a tandem OLED. The tandem OLED has at least two light emitting units, between which a metal layer or an n-type doping organic layer, etc., may be disposed.
The ideal metal layer is extremely thin and capable of filming. However, in actual process, the excessively thin metal layer, when used for fabricating a relatively large-sized panel, is apt to cause a problem of uniformity for its too small thickness, and even render the tandem OLED unable to function properly. If the metal layer is made too thick, its penetrability will be reduced; and when the metal layer is even thicker, a problem of lateral conductivity will be caused.